1. An oxide is a chemical compound made up of at least one oxygen atom and one other element which can be a metal or a non-metal.

2. The reaction between an element and oxygen is known as an oxidation reaction. The opposite reaction, where oxygen is removed from an oxide is called reduction.

3. Metal oxides are solids at room temperature and, if soluble, dissolve to form alkaline solutions. Non-metal oxides are usually gases and dissolve to form acidic solutions.

4. Rust is a hydrated form of iron oxide (Fe₂O₃). It is formed when iron (or steel) is exposed to the air and moisture.

5. Aluminium forms a coating of aluminium oxide which protects the metal and makes it resistant to corrosion.

6. Carbon dioxide (CO₂) is an example of a non-metal oxide. It reacts with water to form carbonic acid. Rainwater is naturally acidic because of this reaction.

7. Carbon monoxide (CO) is a toxic gas. It binds with haemoglobin in red blood cells reducing its ability to carry oxygen around the body.

8. The crystalline form of aluminium oxide (Al₂O₃) is known as corundum. Naturally it is clear but when mixed with impurities it forms beautifully coloured gemstones. The blue variety is sapphire and the red, ruby.

9. Water is an oxide formed from oxygen and hydrogen. It has the formula H₂O and so is technically known as dihydrogen monoxide.

10. Most ores contain metal oxides. To extract the metal the oxide is reduced to remove the oxygen. For metals less reactive than carbon, carbon can be used as the reducing agent.

11. Nitrogen oxides (mainly NO and NO₂) are produced inside car engines. Temperatures are high enough to react the normally inert nitrogen with oxygen.